Tumoral melanosis (TM) is a histological reaction pattern consisting of nodular accumulation of pigment-laden macrophages in the dermis. TM is a regressive phenomenon, secondary to a variety of conditions associated with dermal deposition of melanin-containing cells. Current literature indicates that high percentage of cases of TM represent melanoma regression. Different designations have been given in the past to this condition. These include: nodular melanosis, melanophagic dermatitis or melanophagocytosis.

Definition:Tumoral melanosis (TM) is a nodular or plaque-like accumulation of melanin-laden macrophages, presenting clinically as a pigmented lesion.

Clinical Features:Clinical features of TM presenting as a primary lesion are not well characterized in the literature. The vast majority of cases present clinically as pigmented papules or nodules and are biopsied to rule out malignant melanoma, either as a primary lesion or in search of the primary site in patients presenting with the metastatic disease. In some cases, patientsl have a known melanoma and TM is found in a satellite nodule, or a distant soft tissue or lymph node mass.

Figure 2. Figure shows high power field from a case of TM. Heavy pigmentation obscures the nuclear features of many of the pigmented cells. However, wherever visible, the nuclei are bland and devoid of prominent nucleoli, characteristic of melanoma cells.

Histological features of TM are very unique. It is characterized by the presence of plaques, nodules or masses of heavily pigmented epithelioid cells localized at different levels of the papillary or reticular dermis (Fig.1). At higher power, it is sometimes difficult to visualize nuclear features of pigmented cells without melanin bleaching. When visible, the nuclei are bland with vesicular nuclei with small eosinophilic nucleoli, consistent with the macrophage lineage (Fig. 2). Immunohistochemical stains are important to confirm the nature of pigmented cells. By definition, TM should not contain melanocytes and should not be associated with melanocytic or other epithelial proliferation or neoplasm. Thus, in TM pigmented cells are negative for S-100 and HBM-45. They are positive for macrophage markers such as CD68. Due to heavy pigmentation bleached sections sometimes have to be used in order to allow interpretation of peroxidase reaction-based immunohistochemical stains. Interpretation of immunohistochemical stains can be facilitated by employing red alkaline phosphatase-detection assays.

Treatment:Unless proven otherwise cases of true TM should be managed as regressed melanomas. Careful follow-up including oncological evaluation should be advised until the primary cause of TM can be identified. In patients with known primary melanoma, the appearance of new nodules of TM, should be interpreted as regressed metastases, with appropriate consequence for staging of the disease.